Photo resists are a number of light sensitive materials commonly used in industrial processes. In the semiconductor industry photo resist is applied to a substrate (circuit board or wafer) and then exposed with light through a mask. The photo resist is then developed via exposure to a chemistry that will remove a portion of the resist. The result is a substrate partially protected by photo resist and partially exposed. The substrate then sees additional processing (etching, plating . . . ). At some point the photo resist no longer has a purpose and needs to be removed. Solvents are typically employed to remove the resist from the substrate. The solvent is typically collected for re-use. Post strip the substrate is rinsed and then dried. The substrate is ready for the next step in the manufacturing process.
Dry Film is one such material with light sensitive properties. It is commonly used in the microelectronic industries for circuit board or semiconductor manufacturing. It is superior to liquid resists at providing thick, uniform films that permit increased pattern density. There are a number of dry films products from a number of manufacturers; likewise there is a variety of chemistries that are used to strip the dry film from the substrate.
Dry films are comprised of a number of components. A partial list includes: monomers, binding agents, photo initiators, stabilizers, plasticizers, anti halation agents and dyes. These components vary widely in their ability to dissolve in chemistry and the chemistries used to strip dry films vary in their ability to dissolve components of dry film.
Solvent that is used to strip the dry film will partially dissolve the dry film. Those components that are not dissolved will range from chunks of un-dissolved dry film to a gelatinous sludge. These materials will clog filters, strainers and piping for tools designed to handle standard soluble photo resist after a small number of substrates are processed. The strip tool must be shut down and manually cleaned. The un-dissolved material must be removed in order to resume operations. Dry film debris and solvents used to remove dry film have serious health concerns. Manually cleaning up dry film strip residue is extremely un-desirable and outright prohibited at some locations. The cost for replacing filters or filter elements is high.
Due to the large quantities, dimensions and viscosity of the residual material the space provided for plumbing is disproportionately large. Larger diameter piping and an increase in number and size of strainers and filters results in larger dimensioned tools than for standard photo resist. Typical semiconductor manufacturing is conducted with low contaminate clean rooms that are expensive to build and operate. Therefore oversized equipment directly translates to increased operational cost.